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Chemistry A Level > REQUIRED PRACTICAL 4 - ID tests > Flashcards

REQUIRED PRACTICAL 4 - ID tests Flashcards

1
Q

Calcium Ca2+ flame colour

A

brick red

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2
Q

Strontium Sr2+ flame colour

A

Red

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3
Q

Barium Ba2+ flame colour

A

Pale green

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4
Q

Observation of halides with Acidified silver nitrate

A
  • Flouride = no ppt too soluble
  • Chloride = white ppt
  • Bromide = cream ppt
  • Iodide = yellow ppt
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5
Q

How to test for halides

A
  1. Dissolve spatula in measure of sample of dilute HNO3 and add few cm3 of dilute or conc ammonia
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6
Q

Observations of halides with DILUTE ammonia

A
  • Chloride = dissolves to form colourless solution
  • Bromide = ppt does not dissolve
  • Iodide = ppt does not dissolve
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7
Q

Observations of halides with CONC ammonia

A
  • Chloride dissolves to form colourless solution
  • Bromide = dissolves to form colourless solution
  • Iodide = ppt does not dissolve
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8
Q

Ionic equations for halides reactions with acidified silver nitrate

A
  • Ag+(aq) + Cl-(aq) —> AgCl(s)
  • Ag+(aq) + Br-(aq) —> AgBr(s)
  • Ag+(aq) + I-(aq) —> AgI(s)
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9
Q

Why does the silver nitrate solution have to be acidified?

A

To remove other ions which would interfere with the test like OH- or sulphite ions

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10
Q

Why is HCl acid not used to acidify the AgNO3 reaction

A

Cl- would react with silver ion Ag+ to form white ppt and form flase positive result

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11
Q

How to get pure dry sample of salt

A
  1. Filter to remove the solid from soluble products
  2. Wash to remove any insoluble purities
  3. Dry to remove water
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12
Q

Purity test

A
  • Melting point test
  • Pure substances melt at fixed melting point
  • Impure substances melt over range of temperatures
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13
Q

Trend down group 2 solubility with NaOH

A

Increases down group 2 (white ppt-> slight white ppt -> colourless solution)

Mg(OH)2 is insoluble

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14
Q

Barium chloride with any amount of NaOH

A

remains colourless

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15
Q

Magnesium chloride with NaOH

A
  • Colourless to slightly white ppt when limited NaOH used
  • Colourless to white ppt when excess used
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16
Q

Calcium bromide with any amount of NaOH

A

colourless –> slightly white ppt

17
Q

Strontium chloride with any amount of NaOH

A
  • Colourless to slightly white ppt
18
Q

Trend down group 2 solubility with H2SO4

A
  • solubility decreases
  • BaSO4 is white ppt and solubility increases down the group
19
Q

Barium chloride with any amount of H2SO4

A

White ppt

20
Q

Strontium chloride with any amount of H2SO4

A

White ppt

21
Q

Calcium bromide with any amount of H2SO4

A

Slight white ppt

22
Q

Magnesium chloride with H2SO4

A
  • With limited H2SO4 slightly white ppt
  • With excess remains colourless solution
23
Q

Test for ammonia solution

A
  • Place ammonium chloride + NaOH + warm releases NH3
  • Forms ammonia gas which is a weak base and turns damp red litmus paper blue
24
Q

Test for strong base (NaOH) and weak base (NH3 solution)

A
  • For both damp red litmus paper goes blue
  • Using a pH meter you will get a different reading NaOH = pH 13/14 and NH3 pH = 8-10
25
Q

Test for carbonate ions CO3(2-) or HCO3-

A
  • Add sample of hydrogen carbonate salt to acid and ensure the gas is bubbled into limewater
  • Effervescence and solid disappears
  • Turns cloudy if CO2 given off
26
Q

Test for sulfates

A
  • Dissolve sulfate salt in dilute HNO3 and add few cm3 of barium chloride
  • White ppt forms = BaSO4
27
Q

KCL, KBr and KI with conc sulfuric acid

A
  • KCl effervescence
  • KBr effervescence and brown gas produced, solution turns deep brown
  • KI solution goes deep brown immediately and brown gas produced
28
Q

Paper test for KCl

A

Damp litmus paper turns red

29
Q

Paper test for KBr

A

Damp K2Cr2O7 paper orange changes to green in presence of SO2 gas

30
Q

Paper test for KI

A

Damp lead nitrate paper turns black in presence of H2S

Chemistry A Level (25 decks)

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